The last several years have seen an increase in the number of occurrences of contamination of aquatic systems with harmful bacteria and/or toxic substances. When such contaminations occur, it is paramount that the effects of such contamination be studied. One method of characterizing the exposure and effects of aquatic system contamination is by sampling sediment in a contaminated region and then performing tests on the sediment in a laboratory environment. This process typically involves taking multiple sediment samples from a particular location at specific time intervals, removing the samples from the sampling location, and adding the sediment samples to beakers or aquaria in a laboratory at a later time period. Test organisms are then added and tests are conducted for a specific time period under strictly controlled laboratory conditions using standardized toxicity testing protocols. The above sediment contamination assessment approach is well established, but does not sufficiently represent the true exposure effects to aquatic communities, particularly when the source of contamination is ephemeral or the exposure varies over time and with ambient conditions.
Alteration of exposure due to sampling and manipulation of samples in preparation for laboratory testing is problematic. Sediment sample manipulation removes the natural stratification that affects exposure to test organisms and also may result in degradation, volatilization, or other alterations of contaminants that occur with exposure to air. When samples are removed from the field, they undergo a variety of physical and chemical changes, which may alter the bioavailability and toxicity of any contaminants they possess. Such alteration may possibly result in false conclusions. Further, laboratory tests may overestimate toxicity due to increasingly higher concentrations of toxicants in the static overlying water, as toxicants desorb from the sediment. Thus, results from laboratory exposures are not necessarily indicative of what is encountered by natural populations in the field.
Additionally, various water quality characteristics unique to each field site also affect the availability of contaminants for uptake by organisms and potential for biological effects (e.g. toxicity). Such water quality characteristics are removed or changed by conducting testing in a laboratory. However, even when the testing is conducted in situ, these water quality characteristics are typically measured either on discrete samples (non-continuous monitoring), or the sensors are placed adjacent to the test chambers themselves, resulting in measurements that may be different from conditions encountered by the test organisms.
A need exists for an improved system for assessing the true exposure and effects of a toxic contaminant on an aquatic environment.